Why "Happy Holidays"?

​Between 1 November and 15 January, there are at least 25 holidays or Holy days celebrated by Buddhists, Christians, Hindus, Jews, Muslims, Seculars, Sikhs, Wiccans, and Merchants. Here are the ones I found. All are Christian except where noted.
 
All Saints’ Day, All Souls' Day, Guru Nanak Birthday (Sikh), Bodhi Day (Buddhist), Diwali/Deepavali (Hindu), Christ the King, Guru Tegh Bahadur Martyrdom (Sikh), Thanksgiving (multiple), Black Friday (merchants), Cyber Monday (merchants), First Day of Advent, St. Andrew’s Day, St. Nicholas Day, Feast of the Immaculate Conception, Feast of Our Lady of Guadalupe, Last day of Chanukah (Jewish), Solstice (Wiccan, others), The Prophet’s Birthday/Milad un Nabi (Islam), Festivus (secular), Christmas, Kwanzaa (multiple), Boxing Day (secular) & Holy Innocents, New Year’s Eve (multiple) /Watch Night, New Year’s Day (multiple and those recovering from New Year's Eve), Epiphany, Eastern Orthodox Xmas, Orthodox New Year, Makarsankranti/Pongal (Hindu).
 
Some people may celebrate none of these, and I may have missed a few in my research.
 
Therefore, in the Spirit of the Season (Autumn, approaching Winter) I wish everyone “Happy Holidays.”
 
I enjoy the gift giving, parties, drinking, and dinners associated with various holidays. I enjoy the spirit of goodwill that accompanies some holidays. I also believe in the phrase from a popular song, “…be good for goodness sake.” Be good because being good is good. Do the right thing not because you fear punishment if you don’t or reward if you do, but do the right thing because it is the right thing.
 
As I look over the list of holidays and Holy Days, and think of the various religious beliefs that underlie many of them, I am reminded of words of John Stuart Mill in his essay, On Liberty: “The same causes that make a person an Anglican in London would make him a Buddhist or a Confucian in Peking.”
 
What Mill was suggesting is that beliefs are inculcated in children, frequently through repetition and memorization (I think of the “Child’s Catechism” which I memorized). We know, or should know, that once an idea is planted in a person’s mind, especially before the person is really capable of independent thought, it is very difficult to change that idea. Our minds build walls behind which ideas hide. Information that supports that idea easily penetrates the wall. Information which contradicts the idea not only is blocked by the wall (perceptual filters) but also makes the wall stronger.
 
To paraphrase Mill: The idea that truth always triumphs is one of those pleasant falsehoods which we repeat until they pass into aphorisms, but which all experience refutes.